5G NGAP - Handover Cancel

Message Fact Sheet

Protocol	ngap	Network	5g
Spec	3GPP TS 38.413	Spec Section	Clause 8.4.5, clause 8.4.5.1, clause 8.4.5.2, clause 8.4.5.3, clause 8.4.5.4, clause 9.2.3.11, and clause 9.2.3.12 (Release 18 baseline)
Direction	Source NG-RAN node -> AMF	Message Type	UE Mobility Management Message

Full message name	5G NGAP - Handover Cancel
Protocol	NGAP
Technology	5G
Direction	Source NG-RAN node -> AMF
Interface	N2 / NG-C
Signaling bearer / channel	UE-associated NGAP signaling / SCTP carried NGAP initiatingMessage from source NG-RAN to AMF in the Handover Cancellation procedure
Typical trigger	The source NG-RAN decides that an already ongoing handover should not continue and asks the AMF to cancel it.
Main purpose	Tells the AMF that an already ongoing handover should be cancelled, identifies the UE context involved, and provides the mandatory Cause that explains why the source side aborted the handover.
Main specification	3GPP TS 38.413, Clause 8.4.5, clause 8.4.5.1, clause 8.4.5.2, clause 8.4.5.3, clause 8.4.5.4, clause 9.2.3.11, and clause 9.2.3.12 (Release 18 baseline)
Release added	Release 15
Procedures where used	Handover Cancellation, Source-side cancellation of ongoing handover, UE mobility management, Controlled termination of handover path

What is Handover Cancel in simple terms?

Handover Cancel is the source-NG-RAN-to-AMF message used in the Handover Cancellation procedure to stop an ongoing handover before completion.

Tells the AMF that an already ongoing handover should be cancelled, identifies the UE context involved, and provides the mandatory Cause that explains why the source side aborted the handover.

Why this message matters

Handover Cancel is the source NG-RAN telling the AMF that an already ongoing handover should be stopped.

Where this message appears in the call flow

Source-side cancellation of an ongoing handover

5G NGAP flow showing the source NG-RAN sending Handover Cancel to the AMF to stop an ongoing handover — Cancellation branch: the source side tells the AMF that the ongoing handover should no longer continue.

Call flow position: A handover has already started, but before successful completion the source NG-RAN asks the AMF to stop the ongoing mobility branch.

Typical state: The source still has the UE context and the handover is active, but the normal success path should no longer continue.

Preconditions:

An ongoing handover exists for the UE.
The source NG-RAN still has the source-side UE context.
The source side has decided the handover must be cancelled before completion.

Next likely message: Handover Cancel Acknowledge from the AMF confirming that the ongoing handover was cancelled

Source cancels the ongoing handover

Cancellation is acknowledged by the AMF

5G NGAP flow showing Handover Cancel from the source NG-RAN followed by Handover Cancel Acknowledge from the AMF — Paired branch: the AMF confirms the cancellation with Handover Cancel Acknowledge.

Cancellation is distinct from target-side failure

5G NGAP flow contrasting source-side Handover Cancel with a separate target-side failure branch — Direction branch: Handover Cancel is source-side cancellation of an ongoing handover, not target-side failure reporting.

Call flow position

Previous message(s): Ongoing handover in progress, Source-side UE context still active, Source-side decision to stop continuation

Next message(s): AMF confirms the request, Handover branch ends for this attempt, The ongoing handover is no longer treated as active

Message direction and transport

Sender and receiver: Source NG-RAN node -> AMF

Interface: N2 / NG-C

Domain: UE mobility management and source-side handover cancellation

Signaling bearer: UE-associated NGAP signaling

Logical channel: SCTP carried NGAP initiatingMessage from source NG-RAN to AMF in the Handover Cancellation procedure

Transport / encapsulation: NGAP over SCTP/IP between source NG-RAN and AMF

Security context: The message runs on an existing UE-associated handover context while the handover is still ongoing. Its role is controlled source-side cancellation rather than target-side failure reporting or successful completion.

Message Structure Overview

Handover Cancel is the source-NG-RAN-to-AMF request to cancel an ongoing handover.
Its payload is minimal but important: the UE identity pair plus a mandatory Cause.
The message does not report target-side rejection and does not signal successful completion.
Operationally, it is the controlled source-side stop signal for an already active handover branch.
The expected paired response is Handover Cancel Acknowledge from the AMF.

ASN.1 for 5G NGAP - Handover Cancel

HandoverCancel ::= SEQUENCE {
  protocolIEs ProtocolIE-Container { {HandoverCancel-IEs} },
  ...
}

HandoverCancel-IEs NGAP-PROTOCOL-IES ::= {
  { AMF UE NGAP ID, mandatory } |
  { RAN UE NGAP ID, mandatory } |
  { Cause, mandatory },
  ...
}

How to read this ASN.1

Decode Handover Cancel in a straightforward order: first match the AMF UE NGAP ID and RAN UE NGAP ID to the active source-side handover context, then read Cause to understand why the source side aborted the ongoing move.

5G NGAP - Handover Cancel - Example Dump

NGAP-PDU
  initiatingMessage
    procedureCode: id-HandoverCancel
    criticality: reject
    value: HandoverCancel
      protocolIEs:
        - id: id-AMF-UE-NGAP-ID
          value: 0x10A1
        - id: id-RAN-UE-NGAP-ID
          value: 0x0041
        - id: id-Cause
          value:
            radioNetwork: handover-cancelled

How to read this dump

Treat this as a teaching example based on the spec structure, not as a captured trace.
The message is intentionally compact because it only needs to identify the handover attempt and explain why the source side is cancelling it.
Read it together with the later Handover Cancel Acknowledge to confirm that the ongoing handover was actually cancelled.

Important Information Elements

IE	Required	Description
`Message Type`	Yes	Identifies the NGAP PDU as Handover Cancel.
`AMF UE NGAP ID`	Yes	Mandatory AMF-side UE identifier used by the AMF to map the cancellation to the correct UE context.
`RAN UE NGAP ID`	Yes	Mandatory source-side UE identifier used to tie the cancellation to the correct source NG-RAN UE context.
`Cause`	Yes	Mandatory reason the ongoing handover is being cancelled. This is the first field engineers should inspect in traces.

Detailed field explanation

`Message Type`

Identifies the NGAP PDU as Handover Cancel.

Presence: Required

In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.

`AMF UE NGAP ID`

Mandatory AMF-side UE identifier used by the AMF to map the cancellation to the correct UE context.

Presence: Required

In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.

`RAN UE NGAP ID`

Mandatory source-side UE identifier used to tie the cancellation to the correct source NG-RAN UE context.

Presence: Required

In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.

`Cause`

Mandatory reason the ongoing handover is being cancelled. This is the first field engineers should inspect in traces.

Presence: Required

In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.

What to check in logs and traces

Confirm Handover Cancel is sent by the source NG-RAN to the AMF, not by the target side.
Match AMF UE NGAP ID and RAN UE NGAP ID to the expected ongoing handover context.
Decode Cause first because it explains why the source side aborted the handover.
Verify Handover Cancel Acknowledge follows from the AMF.
Keep this cancellation path distinct from Handover Failure and Handover Preparation Failure.

Common Issues and Troubleshooting

Engineers confuse source-side cancellation with target-side handover failure.

Likely cause: Several handover messages describe unsuccessful outcomes, but they belong to different senders and phases.

What to inspect: Check direction first. Handover Cancel is source NG-RAN to AMF, while Handover Failure is target NG-RAN to AMF and Handover Preparation Failure is AMF to source NG-RAN.

Next step: Map the event to the correct sender and branch before interpreting Cause or later behavior.

The trace looks like a completed handover, but a cancellation message appears.

Likely cause: Reviewers may read Handover Cancel as a late status report instead of a request to stop an ongoing handover.

What to inspect: Verify whether the source-side context was still active and whether Handover Cancel Acknowledge followed.

Next step: Treat the branch as controlled cancellation rather than successful completion.

The wrong UE seems to have been cancelled in multi-attempt mobility traces.

Likely cause: The identity pair may be mixed up with another handover attempt for the same UE.

What to inspect: Correlate both AMF UE NGAP ID and RAN UE NGAP ID together, not one identifier alone.

Next step: Rebuild the exact handover timeline around the specific identity pair before drawing conclusions.

LTE / 5G / Variant Comparison

Compared with Handover Cancel Acknowledge

Handover Cancel is the source-side request to cancel the ongoing handover. Handover Cancel Acknowledge is the AMF confirmation that the cancellation took effect.

Compared with Handover Failure

Handover Failure is a target-side resource-allocation failure report. Handover Cancel is a source-side request to stop an already ongoing handover.

Compared with Handover Preparation Failure

Handover Preparation Failure is the AMF-to-source unsuccessful outcome of preparation. Handover Cancel is initiated by the source after the handover is already ongoing.

FAQ

What is Handover Cancel in 5G NGAP?

It is the source-NG-RAN-to-AMF message used to cancel an ongoing handover before completion.

Who sends Handover Cancel?

The source NG-RAN node sends Handover Cancel to the AMF.

When is Handover Cancel used?

It is used when the source side decides that an already ongoing handover should no longer continue.

What does the Cause IE mean in Handover Cancel?

Cause is the mandatory explanation of why the source side cancelled the ongoing handover.

What is the difference between Handover Cancel and Handover Failure?

Handover Cancel is a source-side cancellation request for an ongoing handover, while Handover Failure is a target-side failure report during resource allocation.

What is the response to Handover Cancel?

The AMF responds with Handover Cancel Acknowledge to confirm that the ongoing handover was cancelled.

Is Handover Cancel sent by the source or target NG-RAN?

It is sent by the source NG-RAN node.

What UE identifiers are mandatory in Handover Cancel?

AMF UE NGAP ID and RAN UE NGAP ID are both mandatory.

Related message pages

Related Procedures

N2 handover

Related Tools

Use This Reference in Practice

Decode this message with the 3GPP Decoder, inspect the related message database, or open the matching call flow to see where this signaling step fits in the full procedure.